add license_header.txt

license_header.txt

@@ -0,0 +1,15 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Parity-Bridge.
+
+// Parity-Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity-Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity-Bridge.  If not, see <http://www.gnu.org/licenses/>.